1. Field of the Invention
The present invention relates generally to techniques which are used during the fabrication of semiconductor devices. More specifically, the invention relates to a technique which uses multiple mappings of critical dimensions of selected features formed on a wafer during the process of forming integrated circuits, to enable tool set calibration/qualification in an efficient manner and with particular regard to mitigating effects which are encountered during the various steps which are carried during the constructive processes.
2. Description of the Related Art
When a new tool set, which should be understood throughout the disclosure to mean at least the combination of a stepper, a wafer track an associated apparatus for moving the wafers to and from the various production stages and locating the wafer in each of the same, is introduced into an IC production line, a great deal of set-up and adjustment is necessary before the arrangement is ready for regular production. For example, calibration or qualifying of the stepper is necessary before production can begin. It is also necessary to calibrate the operation of the wafer track and associated robotics in order to determine that the wafer is being moved between and disposed in, the stepper and processing chambers (e.g. etching chambers) in an optimally correct manner, and thus assure that the wafer is reproducibly set on the table of the stepper in a correctly oriented and located position.
That is to say, during the fabrication of an IC it is necessary to imprint images on resist coating and to etch, deposit, implant or the like, any number of times before the devices on the wafer are completed. It is therefore necessary to ensure that hardware which is used to move the wafer(s) back and forth, manipulate and to photolithograph, is operating in a manner wherein each and every wafer undergoes the same manipulations/operations during each and every stage of production. For example, accurate reproducible location of the wafer in the stepper is necessary. U.S. Pat. No. 5,392,361 issued on Feb. 21, 1998 in the name of Imaizumi et al., discloses the use of a mark on the wafer and a mark position detecting method and apparatus which uses fuzzy logic to improve alignment accuracy.
For further examples of the type of arrangements which are associated with the tool set reference can be had to U.S. Pat. No. 4,641,071 issued in February 1987 in the name of Tazawa et al, and U.S. Pat. No. 4,719,357 issued in January 1998 in the name of Ayata et al.
However, no matter what measures are taken, in the final analysis, the only way of determining if all of the necessary adjustments have been made in an optimal manner, is to make a test run and to examine the end product (viz., conduct empirical testing). However, this technique tends to leave it to chance as to which adjustment or setting needs to be fine tuned in order to bring this highly complex arrangement into truly optimal operational status. That is to say, the setting and arrangement of the reticle which is set in the optics of the stepper must be carefully examined in order to determine if adjustments to this vital piece of apparatus is necessary to correct some less than desirable outcome of the IC production.
This is a kind of feedback type of approach. An adjustment to the stepper operation the robotics which move the wafers from the wafer track to the stepper table, the position to which the wafer track moves the wafers prior to transfer, in combination with a possible change in the reticle or even in a resist or etching recipe, may, even though it would appear contrary to what might be conventionally considered to be correct and/or appropriate, enable the end result to be improved and, hence, would be highly beneficial.
Nevertheless, without some form of sophisticated analysis which can be carried out in a reliable and reproducible manner, the above types of adjustment and changes in technique amount to nothing more than guess work. Accordingly, there remains a need for a reliable technique via which a new tool set can be introduced and qualified in a manner which identifies the problems which need to be addressed in order to achieve set-up quickly and relatively inexpensively.